Under certain conditions, some tractors, including 4 wheel drive tractors, can experience an instability known as “power hop”. During a power hop event, the tractor is excited and begins to jump and bounce during field operations due to specific soil and tire interactions. Once power hop is excited, it continues to build in amplitude until the operator reduces speed, raises the implement or stops. Power hop decreases ride comfort and causes loss of traction. Traditionally the operator would have to adjust ballast and/or tire pressure to attenuate the power hop. It is desired to provide an axle suspension system for a four wheel drive articulated tractor which allows attenuation of power hop so that ride comfort can be improved.